Rotary heat exchangers with corotating, coaxial evaporator and condenser sections have been disclosed, for example, in my U.S. Pat. No. 3,811,495 and applications Ser. No. 234,433 filed March 13, 1972 (now Pat. No. 3,888,304), Ser. No. 286,569 filed Sept. 5, 1972 (now Pat. No. 3,877,515, and Ser. No. 383,537 filed July 30, 1973. In all these instances the two heat-exchanger sections are formed by tubes extending parallel to the axis of rotation in an annular array centered on that axis, these tubes being interconnected in a closed circuit containing a vaporizable working fluid. Circulation of the working fluid can be maintained by a pump and/or by centrifugal action.
If the thermodynamic machine operates as a heat pump, be it for heating or for cooling purposes, a compressor is inserted in the closed circuit downstream of the evaporator section and upstream of the condenser section to raise the temperature of the working fluid, allowing it to give off heat in the condenser section to a surrounding medium (which may be the ambient air) in order to be reliquefied; the compressor, of course, must be powered by an extraneous source. Conversely, if a thermal imbalance is maintained by extraneous means between the condenser section and the evaporator section, the vapors evolving in the latter section can be utilized to drive an expansion motor (e.g. a turbine) with resulting cooling effect. In either instance, conversion of mechanical energy to heat or vice versa occurs substantially adiabatically in the engine unit inserted between the two sections.
The advantage of a rotary evaporator of the aforedescribed type resides in the fact that the working fluid can be distributed in its tubes as a thin film in effective heat-exchanging relationship with the surrounding medium. In certain situations, however, too much working fluid may evaporate in this heat exchanger so that part of its tubes could run dry, thereby significantly impairing the efficiency of the operation; in some instances, especially where the evaporating heat-exchanger section is exposed to the flame of a burner, the local absence of working fluid may cause damage to the evaporator structure.